1. Field of the Invention
The present invention relates to a honeycomb structure, and more particularly, it relates to a honeycomb structure which has a high strength, a large heat capacity and a large thermal conductivity and is therefore hard to be damaged even during use at high temperatures.
2. Description of Related Art
A honeycomb structure is broadly used as a filter which traps particulate matter included in a dust-containing fluid such as an exhaust gas discharged from a diesel engine and removes the particulate matter from the exhaust gas, or a catalyst carrier onto which a catalyst to purify harmful substances (NOx, and the like) in the exhaust gas is to be loaded. In addition, it is known that for the purpose of using such a honeycomb structure under an environment exposed to a high-temperature exhaust gas, refractory particles such as silicon carbide particles are used as a constituent material of the honeycomb structure.
For example, in Patent Document 1, a catalyst carrier is disclosed which is obtained by using silicon carbide (SiC) powder as a starting material, forming this material into a desirable shape and drying the material, followed by firing in a temperature range of 1600 to 2200° C. However, for the catalyst carrier described in Patent Document 1, the very high firing temperature is required, and hence cost is high. In addition, silicon carbide having a high thermal expansion coefficient is fired at the high temperature, and hence, for example, a problem that a firing yield is low is involved sometimes. Additionally, in Patent Document 2, as a honeycomb structure which can inexpensively be manufactured at a comparatively low firing temperature, a honeycomb structure including silicon carbide particles (SiC) and metal silicon (Si) is disclosed. However, as to the honeycomb structure described in Patent Document 2, wettability of silicon carbide to metal silicon is not sufficiently obtained, the honeycomb structure cannot be provided with high strength, and a thermal conductivity of the honeycomb structure is not sufficiently obtained. Therefore, for example, a problem that the honeycomb structure is damaged due to thermal stress is involved sometimes.
Furthermore, in Patent Documents 3 and 4, technologies for an improvement to solve the abovementioned problems of the catalyst carrier and the honeycomb structure are disclosed. That is, in Patent Document 3, a silicon carbide porous body is disclosed which includes silicon carbide particles (SiC) and metal silicon (Si) and in which surfaces or peripheries of the silicon carbide particles and/or metal silicon particles include an alkali earth metal or the like. Additionally, in Patent Document 4, a silicon carbide porous body is disclosed in which silicon carbide particles (SiC) and metal silicon (Si) are bonded in a state where pores are held and part of micropores among the pores has a phase of strontium oxide or the like. Further, according to such constitutions, the wettability of silicon to silicon carbide improves, a contact area between a silicon interface and a silicon carbide interface increases, strength and a thermal conductivity of the silicon carbide porous body improve, and the silicon carbide porous body is hard to be damaged even during use at high temperatures.
[Patent Document 1] JP-A-H06-182228
[Patent Document 2] JP-A-2002-201082
[Patent Document 3] JP-B-4307781
[Patent Document 4] JP-B-4426459